Lead frames are typically made by etching or stamping a metal film to specific shapes and dimensions. Finely configured lead frames often resemble very delicate embroidery, or stencil-like metal structures. Such conventional lead frames are used in the industry to create a variety of chip packages, including wire bonded and flip-chip packages.
Conventional lead frames lack structural rigidity. The finger-like portions of lead frames are quite flimsy and difficult to hold in position during processing. This leads to handling flaws, damage and distortion during assembly processing.
In automated processes for making chip size packages, manufacturers typically form a plurality of interconnected lead frames in a block matrix, attach and electrically connect chips to each lead frame in the block, encapsulate the chip/lead frames, back etch the metal between the contacts of each lead frame and then saw singulate each chip/lead frame to form individual packages. In conventional processes, however, the lead frames in the block are interconnected to one another until the singulation step. During the process of singulating, the thickness of the saw blade cuts not only through the encapsulant plastic, but also through the metal connections that hold the lead frames together in the block. The force and vibration of the saw blade places undue stress on the attachment and electrical connection between the chips and the lead frames. This can lead to structural defects, such as delamination at the metal-plastic interfaces. The present invention overcomes these problems.